The plasma membrane H(+)-ATPase gene family in Solanum tuberosum L. Role of PHA1 in tuberization

This study presents the characterization of the plasma membrane (PM) H(+)-ATPases in potato, focusing on their role in stolon and tuber development. Seven PM H(+)-ATPase genes were identified in the Solanum tuberosum genome, designated PHA1–PHA7. PHA genes show distinct expression patterns in different plant tissues and under different stress treatments. Application of PM H(+)-ATPase inhibitors arrests stolon growth, promotes tuber induction, and reduces tuber size, indicating that PM H(+)-ATPases are involved in tuberization, acting at different stages of the process. Transgenic potato plants overexpressing PHA1 were generated (PHA1-OE). At early developmental stages, PHA1-OE stolons elongate faster and show longer epidermal cells than wild-type stolons; this accelerated growth is accompanied by higher cell wall invertase activity, lower starch content, and higher expression of the sucrose–H(+) symporter gene StSUT1. PHA1-OE stolons display an increased branching phenotype and develop larger tubers. PHA1-OE plants are taller and also present a highly branched phenotype. These results reveal a prominent role for PHA1 in plant growth and development. Regarding tuberization, PHA1 promotes stolon elongation at early stages, and tuber growth later on. PHA1 is involved in the sucrose–starch metabolism in stolons, possibly providing the driving force for sugar transporters to maintain the apoplastic sucrose transport during elongation.